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Seasonic FOCUS PLUS Gold (FX) 850W PSU Review

Correctly testing power supplies is a complex procedure and KitGuru have configured a test bench which can deliver up to a 2,000 watt DC load. We run at 35c in our environment to greater reflect warmer internal chassis conditions.

We use combinations of the following hardware:
• SunMoon SM-268
• CSI3710A Programmable DC load (+3.3V and +5V outputs)
• CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• Extech Power Analyzer
• Extech MultiMaster MM570 digital multimeter
• Extech digital sound level meter
• Digital oscilloscope (20M S/s with 12 Bit ADC)
• Variable Autotransformer, 1.4 KVA

We test in a single +12V configuration.

DC Output Load Regulation

Combined

DC Load

+3.3V
+5V
+12V
+5VSB
-12V
A
V
A
V
A
V
A
V
A V
100W
1.57
3.32
1.76
5.00
6.66
12.04
0.50
5.01
0.20 -12.03
225W
3.75
3.32
3.86
5.00
15.59
12.03
1.00
5.01
0.20 -12.04
450W
7.54
3.31
8.35
4.99
30.78
12.02
1.50
5.00
0.30 -12.04
675W 11.33 3.31 12.35 4.98 47.46 11.98 2.00 5.00 0.50 -12.04
850W
1.52
3.32
1.17
5.00
63.53
11.94
0.50
5.00
0.20 -12.05

Load regulation is stellar with all rails exhibiting very minor fluctuation under load.

Seasonic FOCUS PLUS Gold (FX) 850W
Maximum Load
910W

We managed to get the power supply to deliver 910W before it would shut down, delivering around 60W more than rated specifications.

Next we want to try Cross Loading. This basically means loads which are not balanced. If a PC for instance needs 500W on the +12V outputs but something like 30W via the combined 3.3V and +5V outputs then the voltage regulation can fluctuate badly.

Cross Load Testing +3.3V +5V +12V -12V +5VSB
A V A V A V A V A V
760W 1.0 3.32 1.0 5.00 60.0 11.95 0.2 -12.03 0.50 5.01
165W 15.0 3.29 18.0 4.95 2.0 12.04 0.2 -12.04 0.50 5.01

The power supply dealt with the demanding cross load test very well exhibiting only minor fluctuation. It was tasked with 60A on the +12V rail and it held at 11.95V. The other rails delivered good results also.

We then used an oscilloscope to measure AC ripple and noise present on the DC outputs. We set the oscilloscope time base to check for AC ripple at both high and low ends of the spectrum.

ATX12V V2.2 specification for DC output ripple and noise is defined in the ATX 12V power supply design guide.

ATX12V Ver 2.2 Noise/Ripple Tolerance
Output
Ripple (mV p-p)
+3.3V
50
+5V
50
+12V1
120
+12V2
120
-12V
120
+5VSB
50

Obviously when measuring AC noise and ripple on the DC outputs the cleaner (less recorded) means we have a better end result. We measured this AC signal amplitude to see how closely the unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load +3.3V +5V +12V 5VSB
100W 5 5 10 5
225W 5 5 15 5
450W 5 5 20 5
675W 5 5 25 5
850W 10 5 25 5

Noise suppression results are extremely impressive, hitting 10mV and 5mV on +3.3V and +5V rails respectively. The +12V rail peaks at 25mV under full load conditions. Great results really overall.

Efficiency (%)
100W
88.8
225W
90.7
450W
92.3
675W
91.6
850W 90.4

Efficiency is very good, peaking at 92.3 percent at 50 percent load. This drops to around 90.4 percent at full load.

We take the issue of noise very seriously at KitGuru and this is why we have built a special home brew system as a reference point when we test noise levels of various components. Why do this? Well this means we can eliminate secondary noise pollution in the test room and concentrate on components we are testing. It also brings us slightly closer to industry standards, such as DIN 45635.

Today to test the power supply we have taken it into our acoustics room environment and have set our Digital Sound Level Noise Decibel Meter Style 2 one meter away from the unit. We have no other fans running so we can effectively measure just the noise from the unit itself.

As this can be a little confusing for people, here are various dBa ratings in with real world situations to help describe the various levels.

KitGuru noise guide
10dBA – Normal Breathing/Rustling Leaves
20-25dBA – Whisper
30dBA – High Quality Computer fan
40dBA – A Bubbling Brook, or a Refrigerator
50dBA – Normal Conversation
60dBA – Laughter
70dBA – Vacuum Cleaner or Hairdryer
80dBA – City Traffic or a Garbage Disposal
90dBA – Motorcycle or Lawnmower
100dBA – MP3 Player at maximum output
110dBA – Orchestra
120dBA – Front row rock concert/Jet Engine
130dBA – Threshold of Pain
140dBA – Military Jet takeoff/Gunshot (close range)
160dBA – Instant Perforation of eardrum

Noise (dBA)
100W
<28.0
225W
<28.0
450W
29.8
675W
31.8
850W 35.8

The large fan spins relatively slowly under low to modest load levels. Above 60% the fan spins up to counter rising heat. At full load the fan is clearly audible but never too intrusive.

Temperature (c)
Intake
Exhaust
100W
37
40
225W
38
43
450W
40
50
675W
45
55
850W
47
60

The large fan works well to expel heat out the rear of the chassis. The overall results are very good indeed.

Maximum load
Efficiency
910 watts
90.0

At 910 watts, the efficiency level measures 90.0%. Not a practical situation to be running 24/7, but worth noting.

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